1. Field of the Invention
The present invention relates generally to an opposing field spectrometer of the type which may be utilized to undertake measurements utilizing an electron beam probe and, more specifically, to an opposing field electrode arrangement for generating spherically symmetrical potential lines.
2. Description of the Prior Art
The use of electron beam mensuration technology to conduct voltage measurements at various test points on the surface of a specimen, such as voltage measurements at interconnects and circuit nodes of integrated microelectronic components, requires the use of a spectrometer for secondary electrons.
In such an electron beam mensuration technology, the test points to be measured on a specimen surface are irradiated with a beam of primary electrons, causing the release or emission of secondary electrons. Depending upon the voltage which is present at the test point, the energy distribution function of the secondary electron is altered. This change in the energy distribution function of the secondary electrons can be determined by a spectrometer for detecting such secondary electrons, and thus the voltage which is present at the test point can be ascertained.
An opposing field spectrometer for use in electron beam mensuration technology is disclosed in U.S. Pat. No. 4,460,866.
An electrostatic opposing field spectrometer is described in an article by H. P. Feuerbaum "VLSI Testing Using the Electron Probe" Scanning Electron Microscopy, 285-296, (1979), I. The opposing field spectrometer disclosed therein, however, cannot transmit the entire solid angle distribution of the secondary electrons triggered at the measuring point on the specimen surface, which results in measuring errors primarily from the fact that the electrons obliquely impacting the planar opposing field network can not pass the opposing field lattice under certain conditions, whereas an electron of the same energy moving perpendicular to the opposing field network can pass the opposing field network.
Plies U.S. Pat. No. 4,464,571 discloses an electrostatic opposing field spectrometer having an extraction electrode and an opposing field electrode formed of two spherically symmetrical electrode elements which generate a spherically symmetrical opposing field. This arrangement of opposing field electrodes takes into consideration the solid angle distribution of the secondary electrons triggered at a test point on the specimen surface. The spherically symmetrical electrodes each have a radius of curvature such that the centers are disposed in a plane containing an imaginary source point for the secondary electrons. While the device disclosed in the Plies patent permits transmission of the solid angle distribution of the secondary electrons, it is difficult and involved to manufacture, particularly do to the spherically symmetrical electrodes.